Dual liner capping layer interconnect structure

ABSTRACT

A high tensile stress capping layer on Cu interconnects in order to reduce Cu transport and atomic voiding at the Cu/dielectric interface. The high tensile dielectric film is formed by depositing multiple layers of a thin dielectric material, each layer being under approximately 50 angstroms in thickness. Each dielectric layer is plasma treated prior to depositing each succeeding dielectric layer such that the dielectric cap has an internal tensile stress.

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor integrated circuits(IC's), and more particularly to back-end-of-the-line (BEOL)interconnects structures.

The continuous scaling to smaller dimensions and the introduction oflow-k dielectrics in copper interconnects have caused reliability issuesto become a greater concern in addition to increasing processcomplexity. In semiconductor interconnect structures Electromigration(EM) has been identified as a metal failure mechanism. EM is a seriousreliability concern for very large scale integrated (VLSI) circuits.

Electromigration failure along the Cu/dielectric interface has beenidentified as a major reliability concern for VLSI circuit applications.It has been observed that voiding in the metal line with the masstransport in the Cu line occurring along the interface of thedielectric, for example Si3N4, SiC, and SiC(N,H), capping layer and Cu.Reducing Cu transport and atomic voiding at the Cu/dielectric interfaceis a major objective in the semiconductor industry for reliabilityenhancement.

FIG. 1 is a cross sectional view of a conventional interconnectstructure. A copper interconnect 10 is formed in an inter leveldielectric (ILD) material 20. A compressive capping layer 30 is thenformed over the exposed surface of the interconnect structures 10 andILD 20. In the conventional interconnect structure shown in FIG. 1, asingle compressive capping layer 30 is provided with a single CVDdeposition step. The compressive capping layer is deposited with atypical thickness of approximately 250 Å. The compressive capping layerin this case results in a tensile stress within the Cu interconnect. TheCVD deposition parameters are typically at a pressure of approximately2.4 Torr, temperature of approximately 400° C., and HF power ofapproximately 1,170 Watts, LF power of approximately 130 Watts. The gascomposition and flow rates are typically SiH₄ at approximately 250standard cubic centimeters per minute (sccm), N₂ at approximately 19,000sccm, and NH₃ at approximately 1,300 sccm.

Reducing Cu transport and atomic voiding at the Cu/dielectric interfaceis disclosed in the present invention by creating compressive stressesin the Cu interconnect. In contrast to a Cu interconnect in the priorart with tensile stress, a Cu interconnect with high compressive stressresults in better resistance to electromigration effects. It is alsodisclosed in the present disclosure that depositing a tensile film ontop of the Cu interconnect and/or depositing a compressive film aroundthe Cu interconnect results in high compressive stress in the Cuinterconnect, which is beneficial for improving EM resistance in the Cuinterconnect.

Therefore, an object of the present invention is to provide a hightensile stress capping layer on top of the Cu interconnects in order toreduce Cu transport and atomic voiding at the Cu/dielectric interface.The high tensile dielectric film is formed by depositing multiple layersof a thin dielectric material, each layer being under approximately 50angstroms in thickness. Each dielectric layer is plasma treated prior todepositing each succeeding dielectric layer such that the dielectric caphas an internal tensile stress.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a semiconductor device comprising; adielectric layer with conductive interconnects partially embeddedtherein; and a tensile capping layer in contact with the conductiveinterconnects. The present invention further comprises a compressivecapping layer in contact with the dielectric layer. The semiconductordevice may further comprise a diffusion barrier layer partiallysurrounding the conductive interconnects. The tensile capping layer ispreferably comprised of sequentially deposited layers.

The tensile capping layer is preferably comprised of a material selectedfrom the group consisting of silicon dioxide (SiO₂), silicon nitride(Si₃N₄), and compounds of silicon such as SiC_(x)N_(y)H_(z), where x, yand z are variable percentages. The conductive interconnects arepreferably comprised of a material selected from the group consisting ofaluminum, copper, tungsten, silver, gold, aluminum-copper and nickel.The diffusion barrier layer is preferably comprised of a materialselected from the group consisting of Ta, TaN, Ti, TiN, Ru, RuN, RuTa,RuTaN, W, and WN.

The present invention also provides a method for forming a semiconductordevice, comprising the steps of: providing a dielectric layer withconductive interconnects partially embedded therein; depositing atensile capping layer on the dielectric layer and conductiveinterconnects; performing a plasma treatment on the tensile cappinglayer; removing the portion of the tensile capping layer on thedielectric layer; depositing a compressive capping layer on the tensilecapping layer and the dielectric layer; and removing the compressivecapping layer from the tensile capping layer.

The tensile capping layer is preferably deposited by chemical vapordeposition at a pressure of approximately 7 Torr, a temperature ofapproximately 400° C., and a high frequency power of approximately 600Watts and low frequency power of approximately 0 Watts. The chemicalvapor deposition comprises a gas composition and flow rate of SiH₄ atapproximately 150 sccm, N₂ at approximately 8,000 sccm, and NH₃ atapproximately 2,500 sccm.

The tensile capping layer is preferably a dielectric material selectedfrom the group consisting of silicon dioxide, silicon nitride and acompound of silicon, carbon, nitrogen and hydrogen in the form ofSiC_(x)N_(y)H_(z) where x, y and z are variable percentages.

The plasma treatment is preferably at a pressure of approximately 5Torr, a temperature of approximately 400° C., and a high frequency powerof approximately 500 Watts and low frequency power of approximately 0Watts. The plasma treatment comprises a gas composition and flow rate ofN₂ at approximately 8,000 sccm for approximately 40 seconds. The tensilecapping layer and the plasma treatment are preferably performed in situ.

The compressive capping layer is preferably removed from the tensilecapping layer by chemical mechanical polishing. The tensile cappinglayer is preferably a multiple deposition capping layer deposited on thedielectric layer and the conductive interconnects by a least twosequential deposition and plasma treatment steps.

The present invention also provides a method for forming a semiconductordevice, comprising the steps of: providing a dielectric layer withconductive interconnects partially embedded therein; depositing acompressive capping layer on the dielectric layer and the conductiveinterconnects; removing the portion of the compressive capping layer onthe conductive interconnects; depositing a tensile capping layer on thecompressive capping layer and the conductive interconnects; and removingthe tensile capping layer from the compressive capping layer.

The tensile capping layer is preferably deposited by chemical vapordeposition at a pressure of approximately 7 Torr, a temperature ofapproximately 400° C., and a high frequency power of approximately 600Watts and low frequency power of approximately 0 Watts. The chemicalvapor deposition comprises a gas composition and flow rate of SiH₄ atapproximately 150 sccm, N₂ at approximately 8,000 sccm, and NH₃ atapproximately 2,500 sccm.

The tensile capping layer is preferably a dielectric material selectedfrom the group consisting of silicon dioxide, silicon nitride and acompound of silicon, carbon, nitrogen and hydrogen in the form ofSiC_(x)N_(y)H_(z) where x, y and z are variable percentages. The plasmatreatment is preferably at a pressure of approximately 5 Torr, atemperature of approximately 400° C., and a high frequency power ofapproximately 500 Watts and low frequency power of approximately 0Watts. The plasma treatment comprises a gas composition and flow rate ofN₂ at approximately 8,000 sccm for approximately 40 seconds. The tensilecapping layer and the plasma treatment are preferably performed in situ.

The compressive capping layer is preferably removed from the tensilecapping layer by chemical mechanical polishing. The tensile cappinglayer is preferably a multiple deposition capping layer deposited on thedielectric layer and the conductive interconnects by a least twosequential deposition and plasma treatment steps.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view illustrating a conventionalinterconnect structure.

FIG. 2 is a schematic cross-sectional view illustrating a preferredembodiment of the present invention.

FIGS. 3 through 12 are schematic cross-sectional views illustratingpreferred structures according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is now described in greater detail by referring tothe following discussion and drawings that accompany the presentapplication. The drawings of the present application, which are referredto in greater detail herein below, are provided for illustrativepurposes and, as such, they are not drawn to scale.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

A preferred embodiment of the present invention is illustrated in FIG.2. A multiple deposition tensile capping layer 40 is formed only on thecopper interconnect 10. A single deposition compressive capping layer 41is formed only on the ILD 20 surface. In the present invention speciallytailored CVD deposition parameters and used in conjunction with a postdeposition surface treatment in between capping layer depositions toprovide a tensile stress capping layer on the interconnects. In apreferred embodiment a single deposition will deposit less thanapproximately 50 Å. In a preferred embodiment the multiple layer tensilecapping layer 40 is comprised of at least 3 sequentially deposited andtreated layers.

Referring to FIG. 3 a preferred embodiment of the present invention isdescribed in more detail. FIG. 3 is a cross sectional view of a portionof a microelectronic element or chip in which a plurality of metalinterconnects are provided by a conductive interconnect material 101formed in patterned openings in accordance with an embodiment of theinvention. FIG. 3 illustrates a stage in fabrication in which aninterlevel dielectric layer or “ILD” 102 has been formed.

The ILD 102 material is preferably a low-k material such as SiCOH orSiLK. The ILD 102 material typically has a dielectric constant that isapproximately 4.0 or less, with a dielectric constant of approximately2.8 or less being even more typical. All dielectric constants mentionedherein are relative to a vacuum, unless otherwise noted. Thesedielectrics generally have a lower parasitic cross talk as compared withdielectric materials that have a higher dielectric constant than 4.0.

Within the ILD 102, a plurality of patterned openings are provided,typically in form of line patterns which extend horizontally in adirection of a major surface 105 which is defined by the upper surfaceof the dielectric layer 102, or which extend in a direction parallel tosuch surface. Within each patterned opening, a diffusion barriermaterial 103 is deposited to line the walls and bottom of each opening,after which a conductive interconnect material 101 is deposited to fillthe remaining space within each opening. These steps are followedtypically by a planarization process, such as a chemical mechanicalpolishing (“CMP”) process, which removes any excess metal that contactsthe exposed upper surface 105 of the ILD 102 outside of the patternedopenings.

The conductive interconnect material 101 that fills each opening in thedielectric layer 102 is preferably a metal, for example, a noble metal,that is not prone to destructive corrosion and has good conductiveproperties. However, a few metals and alloys of metals stand out asbeing especially suited for forming conductive interconnect lines in theBEOL fabrication of integrated circuits or chips. Such metals includealuminum, copper, tungsten, silver, gold, aluminum-copper and nickel. Ina particular embodiment, the conductive interconnect material 101 whichfills the patterned opening in the dielectric layer 102 consistsessentially of copper.

When the conductive interconnect material 101 includes copper or othermetal prone to diffusing through dielectric materials, i.e., when themetal has a “high coefficient of diffusion”, the conductive interconnectmaterial 101 is preferably formed over a layer of metal or compound of ametal which functions as a diffusion barrier. The diffusion barriermaterial 103 prevents the copper from diffusing from the conductiveinterconnect material 101 into the ILD 102 adjacent to the walls andbottom of the metal line.

The diffusion barrier material 103 is preferably Ta, TaN, Ti, TiN, Ru,RuN, RuTa, RuTaN, W, WN or any other material that can serve as abarrier to prevent conductive material from diffusing there through. Thediffusion barrier material 103 does not interact with the conductiveinterconnect material 101, such that the barrier layer 103 does notaffect the conductive properties of the conductive interconnect material101 or interact with the dielectric material of the ILD 102 to affectits dielectric properties. Deposition is formed by a deposition processsuch as, for example, atomic layer deposition (ALD), chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD),sputtering, chemical solution deposition, or plating.

The substrate, which is not shown, may comprise a semiconductingmaterial, an insulating material, a conductive material or anycombination thereof. When the substrate is comprised of a semiconductingmaterial, any semiconductor such as Si, SiGe, SiGeC, SiC, Ge alloys,GaAs, InAs, InP and other III/V or II/VI compound semiconductors may beused. In additional to these listed types of semiconducting materials,the present invention also contemplates cases in which the semiconductorsubstrate is a layered semiconductor such as, for example, Si/SiGe,Si/SiC, silicon-on-insulators (SOIs) or silicon germanium-on-insulators(SGOIs).

When the substrate is an insulating material, the insulating materialcan be an organic insulator, an inorganic insulator or a combinationsincluding multilayers thereof. When the substrate is a conductingmaterial, the substrate may include, for example, polySi, an elementalmetal, alloys of elemental metals, a metal silicide, a metal nitride orcombinations including multilayers thereof. When the substrate comprisesa semiconducting material, one or more semiconductor devices such as,for example, complementary metal oxide semiconductor (CMOS) devices canbe fabricated thereon. When the substrate comprises a combination of aninsulating material and a conductive material, the substrate mayrepresent a lower interconnect level of a multilayered interconnectstructure.

Referring now to FIG. 4 there is illustrated the deposition of a firstdielectric capping layer 215. In a preferred embodiment the CVDdeposition parameters are at a pressure of approximately 7 Torr,temperature of approximately 400° C., and HF power of approximately 600Watts, LF power of approximately 0 Watts. The gas composition and flowrates are SiH₄ at approximately 150 sccm, N₂ at approximately 8,000sccm, and NH₃ at approximately 2,500 sccm.

The first dielectric capping layer 215 can include any dielectricmaterial or combination of dielectric materials which is capable ofmaintaining a stress relative to the metal filled line patterns.Preferably, the first dielectric capping layer 215 consists essentiallyof one or more dielectric materials or combinations of dielectricmaterials selected from the group consisting of silicon dioxide (SiO₂),silicon nitride (Si₃N₄), and or other dielectric compound of siliconsuch as SiC_(x)N_(y)H₇, where x, y and z are variable percentages.

After deposition, the first dielectric capping layer 215 is subjected toan extended time, high temperature and high frequency power plasmatreatment, preferably using a combination of ammonia and nitrogenspecies (NH₃ and N₂) or, alternatively, hydrogen (H₂). In a preferredembodiment the plasma treatment parameters are at a pressure ofapproximately 5 Torr, temperature of approximately 400° C., and HF powerof approximately 500 Watts, LF power of approximately 0 Watts. The gascomposition and flow rates are N₂ at approximately 8,000 sccm. Theplasma treatment is for approximately 40 seconds.

The dielectric cap deposition and subsequent plasma treatment arepreferably performed in situ, i.e., in the same process chamber or inthe same tool having one or more connected chambers. In that way, it isperformed without having to manually remove the substrate from thechamber to deposit the dielectric cap after plasma treating the surfaceof the ILD. In a preferred embodiment, a first dielectric cap layer 215is deposited to cover the exposed upper surface 105 of the ILD 102 andthe conductive interconnect material 101 to a thickness of less thanapproximately 50 angstroms. After deposition, the exposed upper surface225 of the first dielectric cap layer 215 is subjected to a secondplasma treatment. The second plasma treatment has the effect ofimparting a tensile stress to the first dielectric cap layer 215.

Referring now to FIG. 5( a) and FIG. 5( b), a second dielectric cappinglayer 226 is deposited to cover the exposed upper surface 225 of thefirst dielectric capping layer 215. Like the first dielectric cappinglayer 215, the second dielectric capping layer 226 preferably is formedto a thickness of less than about 50 angstroms. Like the firstdielectric capping layer 215, the second dielectric capping layer 226can include any dielectric material or combination of dielectricmaterials which is capable of maintaining a stress. Preferably, thesecond dielectric capping layer 226 consists essentially of one or moredielectric materials or combinations of materials selected from thegroup consisting of silicon dioxide, silicon nitride and a compound ofsilicon, carbon, nitrogen and hydrogen in the form of SiC_(x)N_(y)H_(z),where x, y and z are variable percentages.

Preferably, the second dielectric capping layer 226 consists essentiallyof the same dielectric material as the first dielectric cap layer. Likethe first dielectric capping layer 215, the exposed upper surface 230 ofthe second dielectric capping layer 226 also undergoes plasma treatmentafter deposition to control the tensile stress of the deposited seconddielectric capping layer 226, preferably using the same parameters andspecies that are used during the plasma treatment of the firstdielectric capping layer 215. For example, the plasma treatment caninclude a mixture of ammonia and nitrogen, or alternatively, hydrogen asthe reactive species. As in the case of the first dielectric cappinglayer 215, these deposition and plasma treatment processes arepreferably performed in situ.

Further regarding FIG. 5( a) and FIG. 5( b), following deposition andplasma treatment of the second dielectric capping layer 226, a thirddielectric capping layer 236 is deposited to cover the exposed uppersurface 230 of the second dielectric capping layer 226. Like the firstdielectric capping layer 215 and second dielectric capping layer 226,the third dielectric capping layer 236 is formed to a thickness of lessthan about 50 angstroms. Like the first and second dielectric cappinglayers 215, 226, the third dielectric capping layer 236 can include anydielectric material or combination of dielectric materials which iscapable of maintaining a stress. Preferably, the third dielectriccapping layer 236 consists essentially of one or more dielectricmaterials or combinations of dielectric materials selected from thegroup consisting of silicon dioxide, silicon nitride and a compound ofsilicon, carbon, nitrogen and hydrogen in the form of SiC_(x)N_(y)H_(z).

Preferably, the third dielectric capping layer 236 consists essentiallyof the same dielectric material as the first and second dielectriccapping layers. As in the plasma treatments performed to the first andsecond dielectric capping layers, the exposed upper surface 240 of thethird dielectric capping layer 236 also undergoes plasma treatment afterdeposition to control or produce a tensile stress in the thirddielectric capping layer 236, preferably using the same parameters andspecies that are used during the plasma treatment of the first andsecond dielectric capping layers. For example, the plasma treatment caninclude a mixture of ammonia and nitrogen, or alternatively, hydrogen asthe reactive species. As in the case of the first and second dielectriccapping layers, these deposition and plasma treatment processes arepreferably performed in situ.

The purpose of successively depositing the dielectric capping layers andthe plasma treatments is to achieve a tensile dielectric capping layer200 which has an internal tensile stress. The internally tensilestressed dielectric capping layer 200 will exert a compressive stress atthe surface of the conductive interconnect material 101 which itcontacts. As a result, the conductive interconnect material 101, e.g.,copper, is less likely to exert a tensile stress on the metal featuresit contacts, which could then result in the problems described above.

The number of dielectric capping layers that are used and otherparameters associated with their fabrication are not of primaryimportance. Rather, the magnitude and stability of the internal tensilestress of the dielectric capping layer are of greater importance.Therefore, if a single layer of the dielectric capping material isdeposited to have the required internal tensile stress of the desiredmagnitude and properties, then a single such dielectric capping layersuffices. Alternatively, if more than three such dielectric cappinglayers are needed to achieve these properties, then more than three suchdielectric capping layers need to be deposited and plasma treated inaccordance with the method described above. In the preferred embodimentillustrated in FIG. 5( a) and FIG. 5( b), the tensile layer 200 iscomprised of three sequentially deposited layers and accompanying plasmatreatments.

Referring now to FIG. 6 there is illustrated the removal of the portionof the tensile capping layer 200 on the ILD 102 surface by conventionallithography and etching processes. The lithographic process includesapplying a photoresist, exposing the photoresist to a desired pattern ofradiation, and developing the exposed resist utilizing a conventionalresist developer. The etching step may comprise a dry etching process, awet chemical etching process or a combination thereof. The term “dryetching” is used herein to denote an etching technique such asreactive-ion etching, ion beam etching, plasma etching or laserablation.

Referring now to FIG. 7 there is illustrated the deposition of a singlecompressive dielectric layer 416 by conventional processes. The blanketdeposition will deposit the compressive dielectric layer 416 over thetensile dielectric capping layer 200 and re-exposed upper surface 105 ofthe ILD 102.

Referring now to FIG. 8 the structure is illustrated after CMP. Removingthe compressive layer material deposited on the tensile layer 200results in a multiple deposition tensile capping layer 200 formed onlyon the conductive interconnect material 101. A single depositioncompressive dielectric layer 416 is formed only on the ILD 102 surface.In this preferred embodiment the multiple deposition tensile cappinglayer 200 is comprised of three sequentially deposited and treatedlayers.

Referring now to FIG. 9 there is illustrated another embodiment of thepresent invention. As described above a conductive interconnect material101 is formed in an inter level dielectric (ILD) material 102. Therewill typically also be a diffusion barrier material 103 between theconductive interconnect material 101 and ILD 102. There is now depositeda single compressive dielectric layer 416.

Referring now to FIG. 10 there is illustrated the removal of the portionof the single compressive dielectric layer 416 on the conductiveinterconnect material 101 surface by conventional lithography andetching processes.

Referring now to FIG. 11 there is illustrated the deposition of atensile dielectric capping layer 200. The blanket deposition willdeposit the tensile dielectric layer 200 over the compressive dielectriclayer 416 and the conductive interconnect material 101. In thispreferred embodiment the tensile layer 200 is comprised of multiplesequentially deposited layers and accompanying plasma treatments asdescribed in the prior embodiment and illustrated in FIGS. 4 and 5.

Referring now to FIG. 12 the structure is illustrated after CMP.Removing the tensile layer material deposited on the compressive layer416 results in a multiple deposition tensile capping layer 200 formedonly on the conductive interconnect material 101. A single depositioncompressive dielectric layer 416 is formed only on the ILD 102 surface.

It will be apparent to those skilled in the art having regard to thisdisclosure that other modifications of this invention beyond thoseembodiments specifically described here may be made without departingfrom the spirit of the invention. Accordingly, such modifications areconsidered within the scope of the invention as limited solely by theappended claims.

1. A method for forming a semiconductor device, comprising the steps of:providing a dielectric layer with at least one conductive interconnectpartially embedded therein; depositing a compressive capping layer onsaid dielectric layer and said at least one conductive interconnect;removing the portion of said compressive capping layer on said at leastone conductive interconnect; depositing a tensile capping layer on saidcompressive capping layer and said at least one conductive interconnect;and removing said tensile capping layer from said compressive cappinglayer.
 2. The method of claim 1 wherein said tensile capping layer isdeposited by chemical vapor deposition at a pressure of approximately 7Torr, a temperature of approximately 400° C., and a high frequency powerof approximately 600 Watts and low frequency power of approximately 0Watts.
 3. The method of claim 2 wherein said chemical vapor depositioncomprises a gas composition and flow rate of SiH₄ at approximately 150sccm, N₂ at approximately 8,000 sccm, and NH₃ at approximately 2,500sccm.
 4. The method of claim 1 wherein said tensile capping layer is adielectric material selected from the group consisting of silicondioxide, silicon nitride and a compound of silicon, carbon, nitrogen andhydrogen in the form of SiC_(x)N_(y)H_(z) where x, y and z are variablepercentages.
 5. The method of claim 1 wherein said tensile capping layeris a multiple deposition capping layer deposited on said dielectriclayer and said at least one conductive interconnect by a least twosequential deposition and plasma treatment steps.